<!DOCTYPE html>
<html>
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<!-- This file documents the use of the GNU compilers.

Copyright © 1988-2023 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<title>What you can and what you cannot do in +load (Using the GNU Compiler Collection (GCC))</title>

<meta name="description" content="What you can and what you cannot do in +load (Using the GNU Compiler Collection (GCC))">
<meta name="keywords" content="What you can and what you cannot do in +load (Using the GNU Compiler Collection (GCC))">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta name="viewport" content="width=device-width,initial-scale=1">

<link href="index.html" rel="start" title="Top">
<link href="Indices.html" rel="index" title="Indices">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Executing-code-before-main.html" rel="up" title="Executing code before main">
<style type="text/css">
<!--
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
kbd.key {font-style: normal}
span:hover a.copiable-link {visibility: visible}
ul.mark-bullet {list-style-type: disc}
-->
</style>


</head>

<body lang="en_US">
<div class="subsection-level-extent" id="What-you-can-and-what-you-cannot-do-in-_002bload">
<div class="nav-panel">
<p>
Up: <a href="Executing-code-before-main.html" accesskey="u" rel="up"><code class="code">+load</code>: Executing Code before <code class="code">main</code></a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<h4 class="subsection" id="What-You-Can-and-Cannot-Do-in-_002bload"><span>8.2.1 What You Can and Cannot Do in <code class="code">+load</code><a class="copiable-link" href="#What-You-Can-and-Cannot-Do-in-_002bload"> &para;</a></span></h4>

<p><code class="code">+load</code> is to be used only as a last resort.  Because it is
executed very early, most of the Objective-C runtime machinery will
not be ready when <code class="code">+load</code> is executed; hence <code class="code">+load</code> works
best for executing C code that is independent on the Objective-C
runtime.
</p>
<p>The <code class="code">+load</code> implementation in the GNU runtime guarantees you the
following things:
</p>
<ul class="itemize mark-bullet">
<li>you can write whatever C code you like;

</li><li>you can allocate and send messages to objects whose class is implemented
in the same file;

</li><li>the <code class="code">+load</code> implementation of all super classes of a class are
executed before the <code class="code">+load</code> of that class is executed;

</li><li>the <code class="code">+load</code> implementation of a class is executed before the
<code class="code">+load</code> implementation of any category.

</li></ul>

<p>In particular, the following things, even if they can work in a
particular case, are not guaranteed:
</p>
<ul class="itemize mark-bullet">
<li>allocation of or sending messages to arbitrary objects;

</li><li>allocation of or sending messages to objects whose classes have a
category implemented in the same file;

</li><li>sending messages to Objective-C constant strings (<code class="code">@&quot;this is a
constant string&quot;</code>);

</li></ul>

<p>You should make no assumptions about receiving <code class="code">+load</code> in sibling
classes when you write <code class="code">+load</code> of a class.  The order in which
sibling classes receive <code class="code">+load</code> is not guaranteed.
</p>
<p>The order in which <code class="code">+load</code> and <code class="code">+initialize</code> are called could
be problematic if this matters.  If you don&rsquo;t allocate objects inside
<code class="code">+load</code>, it is guaranteed that <code class="code">+load</code> is called before
<code class="code">+initialize</code>.  If you create an object inside <code class="code">+load</code> the
<code class="code">+initialize</code> method of object&rsquo;s class is invoked even if
<code class="code">+load</code> was not invoked.  Note if you explicitly call <code class="code">+load</code>
on a class, <code class="code">+initialize</code> will be called first.  To avoid possible
problems try to implement only one of these methods.
</p>
<p>The <code class="code">+load</code> method is also invoked when a bundle is dynamically
loaded into your running program.  This happens automatically without any
intervening operation from you.  When you write bundles and you need to
write <code class="code">+load</code> you can safely create and send messages to objects whose
classes already exist in the running program.  The same restrictions as
above apply to classes defined in bundle.
</p>


</div>
<hr>
<div class="nav-panel">
<p>
Up: <a href="Executing-code-before-main.html"><code class="code">+load</code>: Executing Code before <code class="code">main</code></a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
